Color filters are generally used in liquid crystal displays (LCDs), optical filters of cameras, and the like, and are prepared by coating a minute area colored with three or more colors onto a charge coupled device or a transparent substrate. Such colored thin films are typically formed by dyeing, printing, electrodeposition, pigment dispersion, inkjet printing, and the like. Currently, such methods are used in the production of LCDs of various electronic devices, such as mobile phones, notebook computers, monitors, TVs, and the like.
In the dyeing method, a colored thin film can be produced by forming an image using a dyeing matrix, such as natural photosensitive resins including gelatin, amine modified polyvinyl alcohols, amine modified acrylic binder resins, and the like, on a glass substrate, followed by dyeing with direct dyes. In order to form a multi-colored thin film on the same substrate, it is necessary to perform flame retardant finishing whenever the color changes, thereby complicating the production process and delaying production time. Although general dyes and resins per se can have good clarity and dispersibility, these dyes and resins have drawbacks in that they can have poor light resistance, moisture resistance, and heat resistance.
In the printing method, a colored thin film can be prepared by printing an ink wherein a pigment is dispersed in a thermosetting or photocurable resin, followed by curing these components with heat or light. This method can reduce material costs as compared to other methods. However, the method has drawbacks in that it can be difficult to form a highly defined and minute image, and the formed thin layers may not be uniform.
Korean Patent Publication No. 1996-0011513 discloses a method of preparing a color filter by inkjet printing. However, this method can result in deteriorated durability and heat resistance as in the dyeing method since a colored photosensitive resin composition to be injected from a nozzle to print a minute and defined color is prepared in dye form.
In the pigment dispersion method, a colored thin film can be produced by repeating a series of steps including coating a photopolymerizable composition containing a colorant on a transparent substrate to which a black matrix is provided, exposing the composition to light in a desired pattern, removing the unexposed portion with a solvent, and heat curing. The pigment dispersion method can enhance heat resistance and durability, which are important properties of color filters, and can ensure a uniform film thickness.
As pigments for color filters in the pigment dispersion method, C.I. Pigment Green, C.I. Pigment Yellow, C.I. Pigment Blue, C.I. Pigment Violet, and the like essentially consisting of phthalocyanine pigments can be used in combination. However, in this case, atomization of the pigments can limit brightness and contrast due to pigment particle size. As a method for additionally improving color properties, it may be necessary to introduce a highly durable dye having no granular property in a molten state or a very small primary particle diameter of not more than several nanometers.
In general, although various studies have been made regarding color filters to which many dyes can be introduced, it is difficult to provide both excellent light transmission and excellent absorption capabilities in a desired color range. Further, dyes satisfying high contrast together with basic reliability for use in color filters are very rare.